The present invention generally relates to a carrier chrominance signal processing circuit, and in particular to a carrier chrominance signal processing circuit for steepening an edge of a carrier chrominance signal to obtain a sharp chrominance signal.
Conventionally, a circuit for steepening a chrominance signal to obtain a sharp picture is known. Such a circuit has been disclosed in Harmut Harlos, "PICTURE SIGNAL IMPROVEMENT IN COLOUR TV RECEIVERS", IEEE Transactions on Consumer Electronics, Vol. CE-31, No.3, pp 156-162, August 1985, for example. The disclosed circuit is intended to detect an edge of each of the color difference signals (R-Y) and (B-Y), and to then hold a signal component at the time of the beginning of the detected edge during a time when the edge is falling or rising. For example, assuming that an edge of an input signal shown in FIG. 1(a) is supplied to the above prior circuit, the circuit holds information on the input signal indicated by a circle "o" during a time indicated by an arrow. After that, the input signal is passed through the circuit at it is. Thereby, an output signal of the circuit as shown in FIG. 1(b) is obtained. As shown, a rising waveform of the output signal has been steepened, or in other words, the edge of the input signal of FIG. 1(a) has been steepened.
However:, the prior circuit is designed so as to process the color difference signals (R-Y) and (B-Y) which are obtained by decoding the carrier chrominance signal. For this reason, the prior circuit cannot handle a carrier chrominance signal as it is. In case where the prior circuit is applied to a system which handles a chrominance signal as a carrier chrominance signal such as a video tape recorder in conformity with a low-frequency band conversion color television system, the carrier chrominance signal must be demodulated, and then the demodulated chrominance signal must be supplied to the prior circuit. Additionally, the output signal of the prior circuit is further modulated in order to supply the steepened chrominance signal to the original signal line. Consequently, a complicated circuit structure is necessary to achieve the above signal processing.